Chromosomal Abnormalities in Philadelphia Chromosome (Ph)-Negative Metaphases Appearing during Imatinib Mesylate (IM) Therapy in Patients (pts) with Newly Diagnosed Chronic Myeloid Leukemia (CML) in Chronic Phase.

The development of chromosomal abnormalities in the Ph-negative metaphases during IM therapy of CML has been recognized mostly in pts who failed prior therapy. Prior exposure to cytarabine has been suggested to be a predisposing factor. This phenomenon has not been yet assessed to date in patients with newly diagnosed CML and treated with IM. This is different from clonal evolution where the abnormalities are observed in the Ph-positive metaphases. We assessed the frequency and the significance of this event among 258 newly diagnosed pts with CML receiving IM (800 mg/d n=207, 400 mg/d n=51) as first line of therapy between March 2001 and April 2005. After a median follow-up of 30 months (range, 6–48 months), 19 pts (7%) developed 21 chromosomal abnormalities in Ph-negative metaphases. Thirteen (62%) of these abnormalities have been seen in 2 or more metaphases. The median time from the start of IM to appearance of abnormalities was 18 months (range, 3–36 months). The most common cytogenetic abnormalities were: loss of chromosome Y (n=7, 33%), trisomy 8 (n=3, 14%), and deletion of chromosome 7 (n=2, 10%). Excluding loss of chromosome Y abnormalities, the incidence was 5%. All pts achieved a major (Ph < 35%) cytogenetic (CG) response (complete cytogenetic response [CCGR] in 17 [89%] pts). Major molecular response (BCR-ABL/ABL ratio <0.05) was observed in 13 (68%) pts (including 2 with complete molecular response). In all but 4 pts these events have been transient and disappeared after a median of 4 months (range, 3–9 months). In 4 pts (loss of chromosome Y n=3, trisomy 8 n=1), they persisted for a median of 13+ months (range, 6+–24+ months). One pt developed acute myeloid leukemia (associated with -7); none of the other pts has any feature of myelodysplasia. After a median follow-up of 13 months (range, 1–42 months), 17 of the 19 pts are alive. One pt died after allogeneic stem cell transplantation, and one died after 6 months of CCGR from myocardial infarction. One pt lost response to IM. The remaining 16 pts are in major CG response at the last follow-up. We conclude that: 1) cytogenetic abnormalities occur in Ph-negative cells in a small fraction of patients (7%; 5% if loss of Y excluded) in newly diagnosed CML on IM; 2) in the majority of cases, they are transient with no clear clinical consequences; 3) in rare instances (loss of chromosome 7 only in our study) they could reflect the emergence of a new malignant clone necessitating and a close follow-up.